Electrorheologic fluids and magnetorheologic fluids are fluids having rheologic properties that can be influenced and controlled by the controlled application of an electric or magnetic field to the fluid. For example, the flow viscosity of the fluid can be varied in a continuous stepless manner from a relatively low viscosity whereby the fluid easily flows when no electrical or magnetic field is applied, to a relatively high viscosity in which the fluid is substantially solid and not flowable when a sufficient electric or magnetic field is applied. Typically, electrorheologic fluids and magnetorheologic fluids are suspensions, and particularly colloidal suspensions of solid particles in a carrier liquid, e.g. an insulating oil, whereby the solid particles are polarizable by means of the applied electric or magnetic field.
Through the use of such electrorheologic or magnetorheologic fluids, also called electroviscous or magnetoviscous fluids, it has become possible to construct various types of actuators without mechanical moving parts, or at least with a significantly reduced number of mechanical moving parts. Moreover, these fluids having a controllable viscosity are also used in applications as diverse as hydraulic valves, hydraulic piston-cylinder devices, vibrators, viscous couplings, shock absorbers, motor bearings, and the like (see the general survey article by R. G. Gorodkin et al., entitled "Applications of the Electrorheological Effect in Engineering Practice", FLUID MECHANICS-Soviet Research, Vol. 8, No. 4, July-August 1979, pgs. 48 to 61).
Electrorheologic fluid actuators typically use an energy conversion device including an arrangement of electrodes for applying a controlled electric field to the electrorheologic fluid that is located between the electrodes. An electric control voltage is then applied to the electrodes. The interaction between the electrode arrangement and the electrorheologic fluid can generally be divided into three categories depending on the type of fluid deformation, respectively corresponding to three basic modes. In the "shear mode", the electrodes are slidingly displaced relative to each other in parallel planes such that the fluid is subjected to shear between the electrodes. In the "flow mode", the electrodes are rigidly and stationarily arranged while the fluid flows between the electrodes. In the "squeeze mode", the electrodes are moved relative to each other so as to change the spacing distance therebetween, thus applying a "squeeze" to the fluid between the electrodes. These different modes may also arise in combination.
A particular example of a mechanical device using an electroviscous fluid is disclosed in German Patent Laying-Open Document 4,003,298 (Andreas Pohl). This publication describes a fluid pump or fluid motor operating according to the displacement principle. The known hydraulic displacement machine includes a vane connected to a rotor that is arranged to rotate in a chamber of a housing. Capacitor plate segments are arranged on the side walls of the chamber, and are connected to electric conductors so that they can be individually electrically energized. The chamber is filled with an electroviscous fluid.
When an electric voltage is applied to the capacitor plate segments in the known hydraulic machine, the electroviscous fluid in the chamber between the capacitor plate segments becomes relatively rigidified to form a blockage. As a result, a suction chamber of the pump is formed between the vane and the blockage on one side, and a pressure chamber of the pump is formed between the vane and the blockage on the other side. As the pump vane rotates in the chamber, fluid is thus sucked into the suction chamber from a suction port and displaced out of the pressure chamber to a pressure port of the pump. In order to maintain the pumping and sucking effect, the electric energization of the condenser plate segments is appropriately controlled to sequentially energize and then de-energize the capacitor plate segments corresponding to the rotation motion of the pump vane on the rotor.
While the hydraulic pump or motor disclosed in German Patent Laying-Open Document 4,003,298 has been shown to be effective for achieving its intended purposes, it has been found that improvements in the output pressure, throughflow volume, efficiency and effective power can be achieved.